who is Ymir
how was he born ?
ymir also know as "aurgelmir" was a giant. Ymir was the father of all the giants. a female and male grew under his arm , and his legs made a 6 headed son . also a cow created buri (grandfather of the great god) he and his brothers later killed Ymir
Where heat and cold met appeared thawing drops, and this running fluid grew into a giant frost ogre named Ymir.
As the ice dripped more, it formed a cow, and from her teats flowed four rivers of milk that fed Ymir. The cow fed on the salt of the rime ice, and as she licked a man's head began to emerge. By the end of the third day of her licking, the whole man had emerged, and his name was Buri. He had a son named Bor, who married Bestla, a daughter of one of the giants. Bor and Bestla had three sons, one of whom was Odin, the most powerful of the gods.
the death of ymir
ymir was killed by the grandfather of the great god odin and his brothers. they killed him and made his corpse the earth. his flesh is the earth , his blood is the oceans and lakes. His bones are the mountains , his hair are the trees. His brain are the clouds
sources
http://norse-mythology.org/gods-and-creatures/giants/ymir/